ASHRAE Journal - December 2009 - 43

concrete) the concrete becomes weak. If the concrete is about 10°C hotter than normal (for example, 30°C, instead of 20°C hotter than normal) the ultimate compressive strength will be about 10% lower.2 The required pouring temperature of concrete varies from site to site (7°C [45°F] to a maximum of 15°C [59°F]). Since the initial and running costs of such a refrigeration system are high, a sophisticated system is essential. Using ice or chilled water in place of some or all of the water during batching is the easiest way to cool concrete during hot weather. Ice or chilled water added to concrete inside the batching plant slightly extends the setting time during hot weather, providing more time to place, consolidate and finish the concrete. Factors influencing the cooling solution include: • Concrete production capacity; • Type of production plant; • Required delivery temperature of the concrete; • Duration of the project; • Available space on the site; • Size of agitator trucks; and • Ambient temperature due to seasonal changes. Concrete Cooling System • Washed sand 25% to 29% • Aggregate (20 micron) 9% to 11% • Aggregate (40 micron) 25% to 29% • Water 6% to 9% Concrete can be cooled to a moderate extent by mixing it with chilled water. The maximum reduction in temperature can be up to 10°C (18°F). The cooling water requirement cannot exceed the mixing water requirement (maximum allowable percentage of water in concrete) and depends upon the moisture content of aggregates and the mixture proportion. The temperature of concrete after mixing with water can be estimated roughly by using Equation 1.4 T = Where Ta = Tc = Tw = Wa = Wc = Ww = 0.22 (Ta × Wa + Tc × Wc ) + Tw × Ww 0.22 (Wa + Wc) + Ww (1) Temperature of Aggregate (including sand) Temperature of cement Temperature of batched mixing water Dry mass of aggregate Mass of cement Mass of batched mixing water A concrete cooling system for dam construction or other massive civil construction generally consists of: • A water chilling plant that produces chilled water (1°C to 2°C [34°F to 36°F]). The quantity may be partly or fully used, according to project requirements. • Cold water tank with pumping station. • Flake ice plant that produces flake ice at –5°C (23°F). • Flake ice storage with fully automatic ice rake and discharge system. • Flake ice delivery system. • Flake ice weighing system. Concrete Cooling Requirements In its simplest form, concrete is a mixture of paste and aggregates. Paste (cement and water) coats the surface with fine coarse aggregates through a chemical reaction called hydration. Paste becomes hard and gains strength gradually, forming a rock-like mass known as concrete. Within this process lies the key to a remarkable trait of concrete: it is plastic and malleable when newly mixed, strong and durable when hardened. These qualities explain why concrete can build skyscrapers, bridges, sidewalks, superhighways, houses and dams. Careful proportioning and mixing of the ingredients is key for achieving strong, durable concrete. A concrete mixture that does not have enough paste to fill all the voids between the aggregates is difficult to place and produces rough/honeycombed surfaces. A concrete mixture with an excess of cement can be easily placed and produces a smooth surface, but the resulting concrete is likely to shrink more than the required percent. Concrete generally contains:3 • Cement 16% to 20% • Dune sand 9% to 12% December 2009 Figure 1 is based on Equation 1 and shows the degree of cooling that we can obtain after using water at 1°C and 4°C (34°F and 39°F). Figure 2 shows refrigeration loads at various water temperatures. The refrigeration load for a given sample of concrete has linear relation between water temperature and refrigeration load per cubed meter per day of concrete. In the Middle East, makeup water temperature is generally high. Average water temperatures vary between 22°C and 26°C (72°F and 79°F) from November to April. Water temperature increases to 30°C (86°F) during summer. If water is stored inside a closed container, the temperature will increase to 35°C (95°F). Increasing the temperature increases the refrigeration load of a concrete cooling system. Figure 3 shows the refrigeration load requirement at 38°C (100°F) (makeup water temperature versus concrete capacity). Water is cooled from 38°C to 4°C (100°F to 39°F). Conventional Water Chilling Plant This plant is used for producing chilled water in the range of 1°C to 2°C (34°F to 36°F). Ammonia or R-22 are generally used as refrigerants. This plant has the following equipment: • Reciprocating compressor or screw compressor; • Water-cooled shell and tube condenser; • Ammonia receiver; • Vertical chiller; • Hot well and cold well chilled water tank; • Primary and secondary chilled water pump; • Cooling tower; • Cooling water pump; • Oil cooler (in case of screw compressor); and • Primary oil separator. ASHRAE Journal 43

ASHRAE Journal - December 2009

Table of Contents for the Digital Edition of ASHRAE Journal - December 2009

ASHRAE Journal - December 2009
Contents
Commentary
Industry News
Letters
Meetings and Shows
ASHRAE Building EQ Program
Feature Articles
A Closer Look at Chiller Ratings
Cooling With Less Air: Using Underfloor Air Distribution and Chilled Beams
Cooling Concrete: Containerized Water Chilling Plant
Geothermal for Community Center
Anniversary Feature: Air-Recovery System Versus Conventional Air Conditioning
Technical Topics
New Product Preview
Products
Emerging Technologies
Washington Report
People
Special Products
2009 Feature Articles Indices
Classified Advertising
Advertisers Index
ASHRAE Journal - December 2009 - ASHRAE Journal - December 2009
ASHRAE Journal - December 2009 - Cover2
ASHRAE Journal - December 2009 - 1
ASHRAE Journal - December 2009 - 2
ASHRAE Journal - December 2009 - Contents
ASHRAE Journal - December 2009 - 4
ASHRAE Journal - December 2009 - Commentary
ASHRAE Journal - December 2009 - Industry News
ASHRAE Journal - December 2009 - 7
ASHRAE Journal - December 2009 - 8
ASHRAE Journal - December 2009 - 9
ASHRAE Journal - December 2009 - 10
ASHRAE Journal - December 2009 - Letters
ASHRAE Journal - December 2009 - 12
ASHRAE Journal - December 2009 - 13
ASHRAE Journal - December 2009 - 14
ASHRAE Journal - December 2009 - 15
ASHRAE Journal - December 2009 - Meetings and Shows
ASHRAE Journal - December 2009 - 17
ASHRAE Journal - December 2009 - Feature Articles
ASHRAE Journal - December 2009 - 19
ASHRAE Journal - December 2009 - 20
ASHRAE Journal - December 2009 - 21
ASHRAE Journal - December 2009 - A Closer Look at Chiller Ratings
ASHRAE Journal - December 2009 - 23
ASHRAE Journal - December 2009 - 24
ASHRAE Journal - December 2009 - 25
ASHRAE Journal - December 2009 - 26
ASHRAE Journal - December 2009 - 27
ASHRAE Journal - December 2009 - 28
ASHRAE Journal - December 2009 - 29
ASHRAE Journal - December 2009 - 30
ASHRAE Journal - December 2009 - 31
ASHRAE Journal - December 2009 - 32
ASHRAE Journal - December 2009 - 33
ASHRAE Journal - December 2009 - Cooling With Less Air: Using Underfloor Air Distribution and Chilled Beams
ASHRAE Journal - December 2009 - 35
ASHRAE Journal - December 2009 - 36
ASHRAE Journal - December 2009 - 37
ASHRAE Journal - December 2009 - 38
ASHRAE Journal - December 2009 - 39
ASHRAE Journal - December 2009 - 40
ASHRAE Journal - December 2009 - 41
ASHRAE Journal - December 2009 - Cooling Concrete: Containerized Water Chilling Plant
ASHRAE Journal - December 2009 - 43
ASHRAE Journal - December 2009 - 44
ASHRAE Journal - December 2009 - 45
ASHRAE Journal - December 2009 - 46
ASHRAE Journal - December 2009 - 47
ASHRAE Journal - December 2009 - Geothermal for Community Center
ASHRAE Journal - December 2009 - 49
ASHRAE Journal - December 2009 - 50
ASHRAE Journal - December 2009 - 51
ASHRAE Journal - December 2009 - Anniversary Feature: Air-Recovery System Versus Conventional Air Conditioning
ASHRAE Journal - December 2009 - 53
ASHRAE Journal - December 2009 - 54
ASHRAE Journal - December 2009 - 55
ASHRAE Journal - December 2009 - 56
ASHRAE Journal - December 2009 - 57
ASHRAE Journal - December 2009 - 58
ASHRAE Journal - December 2009 - 59
ASHRAE Journal - December 2009 - 60
ASHRAE Journal - December 2009 - 61
ASHRAE Journal - December 2009 - Technical Topics
ASHRAE Journal - December 2009 - 63
ASHRAE Journal - December 2009 - 64
ASHRAE Journal - December 2009 - New Product Preview
ASHRAE Journal - December 2009 - 66
ASHRAE Journal - December 2009 - 67
ASHRAE Journal - December 2009 - 68
ASHRAE Journal - December 2009 - 69
ASHRAE Journal - December 2009 - 70
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ASHRAE Journal - December 2009 - 111
ASHRAE Journal - December 2009 - 112
ASHRAE Journal - December 2009 - 113
ASHRAE Journal - December 2009 - Products
ASHRAE Journal - December 2009 - 115
ASHRAE Journal - December 2009 - 116
ASHRAE Journal - December 2009 - Emerging Technologies
ASHRAE Journal - December 2009 - Washington Report
ASHRAE Journal - December 2009 - 119
ASHRAE Journal - December 2009 - People
ASHRAE Journal - December 2009 - Special Products
ASHRAE Journal - December 2009 - 2009 Feature Articles Indices
ASHRAE Journal - December 2009 - 123
ASHRAE Journal - December 2009 - 124
ASHRAE Journal - December 2009 - 125
ASHRAE Journal - December 2009 - Classified Advertising
ASHRAE Journal - December 2009 - 127
ASHRAE Journal - December 2009 - Advertisers Index
ASHRAE Journal - December 2009 - Cover3
ASHRAE Journal - December 2009 - Cover4
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